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Glossary of Glacier Terminology

Calving

The process by which pieces of ice break away from the terminus of a glacier that ends in a body of water or from the edge of a floating ice shelf that ends in the ocean. Once they enter the water, the pieces are called icebergs.


Southwest-looking photograph showing a large calving wave and many recently-calved pieces of ice moving away from the terminus of Johns Hopkins Glacier, following a major calving event, St Elias Mountains, Glacier Bay National Park, Alaska.

Chatter Marks

A series of small, closely spaced, crescentic grooves or scars formed in bedrock by rocks frozen in basal ice as they move along and chip the glacier's bed. The horns of the crescent generally point down glacier.


Close-up photograph of the surface of a recently deglacierized bedrock outcrop adjacent to Yale Glacier, Yale Arm, College Fiord, Chugach Mountains, Chugach National Forest, Prince William Sound, Alaska, showing a series of more than one-half-dozen nested arcuate chatter marks and a number of multi-directional, linear striations. Note the tip of the pen for scale.

Southwest-looking oblique aerial photograph showing a number of snow-covered cirques, cut into the summit of a Coast Mountains ridge along the Alaska - Canada border, east of Glacier Bay National Park, Alaska. Note the uniform snowline.

Cirque

A bowl-shaped, amphitheater-like depression eroded into the head or the side of a glacier valley. Typically, a cirque has a lip at its lower end. The term is French and is derived from the Latin word circus.


North-looking oblique aerial photograph showing an ice and snow-filed cirque in the accumulation area of the Fairweather Range, east of Mount Fairweather, Glacier Bay National Park, Alaska.

Northeast-looking oblique aerial photograph showing several ice and snow-filed cirques on the west flank of Mount Fairweather, Fairweather Range, Glacier Bay National Park, Alaska.

Crescentic Gouge

Any curved mark or fracture produced by plucking or chipping of the glacier's bed. Larger than chatter marks,typically the horns of these gouges point up glacier. Also called Lunate Fracture or Crescentic Mark.


Close-up photograph of the surface of a recently deglacierized bedrock outcrop adjacent to Yale Glacier, in Yale Arm, College Fiord, Chugach National Forest, Prince William Sound, Alaska. It shows an irregularly-shaped, deeply incised crescentic gouge, several nested arcuate chatter marks and a number of multi-directional, linear striations. Note the tip of the pen for scale.

East-looking photograph showing two recently opened crevasses in July 1976 on the surface of Taku Glacier, Juneau Icefield, Tongass National Forest, Coast Mountains, Alaska. The longer of the two crevasses extends for nearly a kilometer.

Crevasse

A crack or series of cracks that open in the surface of a moving glacier in response to differential stresses caused by glacier flow. They range in shape from linear to arcuate, in length from feet to miles. Their orientation may be in any direction with respect to the glacier flow. The deepest crevasses may exceed 100 feet.


northeast-looking oblique aerial photograph showing several parallel and sub-parallel open crevasses on the surface of the piedmont lobe of Bering Glacier, Alaska in July 1994. Perpendicular to the open crevasses are a number of snow-filed crevasses. The snow-filled crevasses formed a year earlier, when this part of the glacier flowed through an area subject to a different stress field. The long crevasse in the center of the photograph extends for nearly 2 miles. Bering Glacier flows through Wrangell-Saint Elias National Park.

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